With engine-driven vehicles, access authorization to the vehicle is subdivided into two separate processes: actual access to the vehicle on the one hand (closing/opening the vehicle by closing/opening the vehicle doors), and starting the vehicle on the other hand (the start process for the vehicle engine, initiated by operating the ignition lock).
Normally, access authorization to the vehicle is provided by mechanical means, that is, by means of a conventional car key. However, increasingly access authorization is also provided by electronic processes and techniques; in such cases, encoded signals will be transmitted between an electronic key and at least one transmission unit located in or on the vehicle (in particular, on the periphery of the vehicle). Thus, for example, encoded signals will be transmitted between an electronic key and a door lock for unlocking the door lock, and/or between a remote control unit and a drive control unit and/or an anti-theft device (a vehicle immobilizer) to release the drive control unit; following evaluation and verification of the signals, as well as meeting specific conditions if necessary, authorized access to the vehicle will be provided.
For these two separate access authorization processes--access to the vehicle on the one hand, and starting the vehicle on the other hand--different operator activities are usually required, as well as different conditions to be met: thus, for example, a vehicle may be started up only if the electronic key is located inside the vehicle; also, for safety reasons, it should only be possible to lock the vehicle doors if the electronic key is located outside the vehicle. Therefore, the two access authorization processes must be differentiated; to this end, the position of the electronic key needs to be determined--in particular, it must be possible to identify its position relative to the vehicle interior and exterior ("interior detection").